Facing state negligence charges Adam Lanza's former psychiatrist gave up his medical license just five months before the Newtown school slaughter.

Medical authorities cited "negligence on more than one occasion" and "possible boundary violations" between Dr. Paul L. Fox and an unidentified patient in the years after Fox -- Lanza's primary psychiatrist during his adolescence-- stopped treating the troubled Sandy Hook teen.

According to the State Police report on the Dec. 14, 2012, massacre of 20 first graders and six adults, Fox said he destroyed his records on Lanza and hadn't seen him for about five years before the shootings.

Psychiatrists are permitted to destroy patient files more than five years old, under state regulations. Investigators quoted Fox, whose practice was in Brookfield, as "vaguely" remembering Lanza and that the only records he kept were on billing information.

"Dr. Fox did recall that Adam was about 15 years of age when he last saw him and recalls Adam having aggression problems and possibly having been diagnosed with Asperger's syndrome," the State Police report said. "He recalled Adam as very rigid and resistant to engagement. He was unable to provide any further details concerning Adam."

More information on the loss of Fox's licenses to practice medicine in Connecticut and New York was not available Saturday. But the voluntary maneuver to surrender his license helped him to avoid the public scrutiny of the Connecticut Medical Examining Board.

Anne Doremus of Manchester, the outgoing chairman of the board, said Saturday that Fox's case did not appear before the panel. Nor does it occur in board minutes.

Fox, a New Fairfield resident at the time, moved to New Zealand and was divorced from Faline Schneiderman, his wife of nearly a quarter century, in June of 2012. A month later, he surrendered his medical credentials in Connecticut and New York.

Attempts on Saturday to reach Fox in New Zealand, where he works in a child social-services program, were unsuccessful. His Hartford lawyer did not return a request for comment.

Kathleen Koenig, a former colleague of Fox's and a nursing professional at the Yale Child Study Center who is familiar with Lanza and his mother Nancy, also declined comment Saturday.

The investigators' reports depict Peter Lanza as much more involved with his son's life and helpful to police than previous news accounts have suggested.

During an interview just two days after the shooting, Peter Lanza was "visibly upset but cooperative" and he tried to help authorities understand more about his son and his motives for the shooting.

Peter Lanza said his son had Asperger's syndrome, but he told investigators that Adam "clearly had some other medical condition" to have done what he did at Sandy Hook Elementary School.

As a young boy, Adam Lanza seemed to be happy and well-adjusted and his father said he enjoyed his time as a student at Sandy Hook. But around the age of 11 or 12, Adam's demeanor changed dramatically. He was now less happy and more stressed and frustrated, although his father said he wasn't angry or aggressive.

Around that same time, Adam became more distant from his older brother, Ryan, and his social interactions became more awkward. Adam mainly communicated with others through games like "World of Warcraft" and "Mario Brothers."

But even as Adam closed himself off to others, his father made an effort to keep in touch with him, emailing him about six to eight times per year. The elder Lanza said his troubled son had stopped responding to his emails in 2010.

Peter Lanza said he last emailed Adam about two or three months before the Sandy Hook shooting. He told police that he hadn't interacted with his son very much in the months leading up to Dec. 14.

He thought his ex-wife, Nancy Lanza, had played a part in Adam's decision to cut off contact with him, he told police.

Two medical professionals at the Yale Child Studies Center who treated Adam Lanza in his teen years gave investigators a dramatic portrait of his psychological problems and his mother's reaction to the treatments.

Dr. Robert A. King and Advanced Practice Registered Nurse Kathleen Koenig both said they had face-to-face meetings with Adam Lanza in late 2006.

It was Koenig who told investigators that Fox was Lanza's primary psychiatrist and she tried to work with him to treat the troubled boy.

King said that Adam Lanza displayed "a lack of comprehension of ordinary social interaction and communications." He said the Newtown school system should do further evaluation of Adam and that Koenig would continue the treatment.

"My concern was that the shooter's social isolation and withdrawal was increasing," the doctor told investigators. But King said he didn't observe anything that could have given any warning that Lanza would one day carry out the shooting at Sandy Hook.

Koenig said Lanza was "emotionally paralyzed" and described several of his bizarre daily rituals, from repeated hand-washing to changing his clothes several times per day, forcing his mother to do three loads of laundry daily.

Adam Lanza was prescribed an anti-depressant called Celexa and Koenig said there should be follow-up visits.

But Nancy Lanza's response was one that Koenig described as "non-compliant."

Immediately after Adam Lanza had been prescribed a small dose of Celexa, Nancy Lanza called Koenig and said her son couldn't raise his arm. Adam blamed the problem on the medication and Nancy said he wouldn't be taking it anymore.

Koenig tried to reason with Nancy Lanza, but she wouldn't listen. She and Adam missed one scheduled follow-up appointment and didn't schedule any more sessions at the Yale center.